With respect to prosecution experts who testify in the form of opinions based upon testimonial hearsay statements, the answer is clear: such opinions should not be permitted. They fall squarely (so to speak) within the three corners of the expert testimonial triangle and sit at the convergence of the various lines of trust and distrust of juries, government, and experts. In other contexts, however, the answers are less clear. Where a government expert relies on evidence that is inadmissible, but not testimonial, Crawford and the Confrontation Clause do not apply and thus only two legs of the triangle are implicated. And with respect to a criminal defendant’s offer of expertise that rests on otherwise inadmissible hearsay, or in civil litigation, the expert testimonial triangle offers not concrete answers but rather directions for further exploration.